Nonaqueous Electrolyte for an Ultracapacitor

ABSTRACT

An ultracapacitor that contains a first electrode, second electrode, separator, nonaqueous electrolyte, and housing is provided. The first electrode comprises a first current collector electrically coupled to a first carbonaceous coating and the second electrode comprises a second current collector electrically coupled to a second carbonaceous coating. The nonaqueous electrolyte is in ionic contact with the first electrode and the second electrode, wherein the nonaqueous electrolyte contains an ionic liquid that is dissolved in a nonaqueous solvent at a concentration of about 1.0 mole per liter or more. The nonaqueous solvent has a boiling temperature of about 150° C. or more.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 62/339,153, filed on May 20, 2016, which is incorporated hereinin its entirety by reference thereto.

BACKGROUND OF THE INVENTION

Electrical energy storage cells are widely used to provide power toelectronic, electromechanical, electrochemical, and other usefuldevices. An electric double layer ultracapacitor, for instance,generally employs a pair of polarizable electrodes that contain carbonparticles (e.g., activated carbon) impregnated with a liquidelectrolyte. Due to the effective surface area of the particles and thesmall spacing between the electrodes, large capacitance values may beachieved. Nevertheless, problems remain. For instance, certaincomponents of conventional ultracapacitors are also sensitive to hightemperatures, which may cause leakage of the electrolyte from thecapacitor, and in turn lead to reduced capacitance and increasedequivalent series resistance (“ESR”). As such, a need currently existsfor an improved ultracapacitor.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, anultracapacitor is disclosed that comprises a first electrode, secondelectrode, separator, nonaqueous electrolyte, and a housing thatcontains a metal container. The first electrode comprises a firstcurrent collector electrically coupled to a first carbonaceous coatingand the second electrode comprises a second current collectorelectrically coupled to a second carbonaceous coating. The separator ispositioned between the first electrode and the second electrode. Thenonaqueous electrolyte is in ionic contact with the first electrode andthe second electrode, wherein the nonaqueous electrolyte contains anionic liquid that is dissolved in a nonaqueous solvent at aconcentration of about 1.0 mole per liter or more. The nonaqueoussolvent has a boiling temperature of about 150° C. or more. The firstelectrode, the second electrode, the separator, and the electrolyte areretained within the housing.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figure in which:

FIG. 1 is a schematic view of one embodiment of a current collector thatmay be employed in the ultracapacitor of the present invention;

FIG. 2 is a schematic view of one embodiment of a currentcollector/carbonaceous coating configuration that may be employed in theultracapacitor of the present invention;

FIG. 3 is a schematic view illustrating one embodiment for forming anelectrode assembly that can be used in the ultracapacitor of the presentinvention; and

FIG. 4 is a schematic view of one embodiment of the ultracapacitor ofthe present invention.

Repeat use of reference characters in the present specification anddrawing is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed an ultracapacitorthat contains a first electrode that contains a first carbonaceouscoating (e.g., activated carbon particles) electrically coupled to afirst current collector, and a second electrode that contains a secondcarbonaceous coating (e.g., activated carbon particles) electricallycoupled to a second current collector. A separator is also positionedbetween the first electrode and the second electrode, and an electrolyteis in ionic contact with the first electrode and the second electrode.The first electrode, second electrode, separator, and electrotype areretained within a housing that is formed from a metal container (e.g.,cylindrical can).

The present inventors have discovered that through selective controlover the particular nature of the nonaqueous electrolyte, a variety ofbeneficial properties may be achieved. More particularly, theelectrolyte is generally nonaqueous in nature and thus contains at leastone nonaqueous solvent. To help extend the operating temperature rangeof the ultracapacitor, the nonaqueous solvent has a relatively highboiling temperature, such as about 150° C. or more, in some embodimentsabout 200° C. or more, and in some embodiments, from about 220° C. toabout 300° C. Particularly suitable high boiling point solvents mayinclude, for instance, cyclic carbonate solvents, such as ethylenecarbonate, propylene carbonate, butylene carbonate, vinylene carbonate,etc. Propylene carbonate is particularly suitable due to its highelectric conductivity and decomposition voltage, as well as its abilityto be used over a wide range of temperatures. Of course, othernonaqueous solvents may also be employed, either alone or in combinationwith a cyclic carbonate solvent. Examples of such solvents may include,for instance, open-chain carbonates (e.g., dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, etc.), aliphatic monocarboxylates(e.g., methyl acetate, methyl propionate, etc.), lactone solvents (e.g.,butyrolactone valerolactone, etc.), nitriles (e.g., acetonitrile,glutaronitrile, adiponitrile, methoxyacetonitrile,3-methoxypropionitrile, etc.), amides (e.g., N,N-dimethylformamide,N,N-diethylacetamide, N-methylpyrrolidinone), alkanes (e.g.,nitromethane, nitroethane, etc.), sulfur compounds (e.g., sulfolane,dimethyl sulfoxide, etc.); and so forth.

The electrolyte also contains at least one ionic liquid, which isdissolved in the nonaqueous solvent. Typically, the ionic liquid ispresent at a relatively high concentration. For example, the ionicliquid may be present in an amount of about 1.0 mole per liter (M) ofthe electrolyte or more, in some embodiments about 1.2 M or more, insome embodiments about 1.3 M or more, and in some embodiments, fromabout 1.4 to about 1.8 M.

The ionic liquid is generally a salt having a relatively low meltingtemperature, such as about 400° C. or less, in some embodiments about350° C. or less, in some embodiments from about 1° C. to about 100° C.,and in some embodiments, from about 5° C. to about 50° C. The saltcontains a cationic species and counterion. The cationic speciescontains a compound having at least one heteroatom (e.g., nitrogen orphosphorous) as a “cationic center.” Examples of such heteroatomiccompounds include, for instance, unsubstituted or substitutedorganoquaternary ammonium compounds, such as ammonium (e.g.,trimethylammonium, tetraethylammonium, etc.), pyridinium, pyridazinium,pyrimidinium, pyrazinium, imidazolium, pyrazolium, oxazolium,triazolium, thiazolium, quinolinium, piperidinium, pyrrolidinium,quaternary ammonium spiro compounds in which two or more rings areconnected together by a spiro atom (e.g., carbon, heteroatom, etc.),quaternary ammonium fused ring structures (e.g., quinolinium,isoquinolinium, etc.), and so forth. In one particular embodiment, forexample, the cationic species may be an N-spirobicyclic compound, suchas symmetrical or asymmetrical N-spirobicyclic compounds having cyclicrings. One example of such a compound has the following structure:

wherein m and n are independently a number from 3 to 7, and in someembodiments, from 4 to 5 (e.g., pyrrolidinium or piperidinium).

Suitable counterions for the cationic species may likewise includehalogens (e.g., chloride, bromide, iodide, etc.); sulfates or sulfonates(e.g., methyl sulfate, ethyl sulfate, butyl sulfate, hexyl sulfate,octyl sulfate, hydrogen sulfate, methane sulfonate, dodecylbenzenesulfonate, dodecylsulfate, trifluoromethane sulfonate,heptadecafluorooctanesulfonate, sodium dodecylethoxysulfate, etc.);sulfosuccinates; amides (e.g., dicyanamide); imides (e.g.,bis(pentafluoroethyl-sulfonyl)imide, bis(trifluoromethylsulfonyl)imide,bis(trifluoromethyl)imide, etc.); borates (e.g., tetrafluoroborate,tetracyanoborate, bis[oxalato]borate, bis[salicylato]borate, etc.);phosphates or phosphinates (e.g., hexafluorophosphate, diethylphosphate,bis(pentafluoroethyl)phosphinate,tris(pentafluoroethyl)-trifluorophosphate,tris(nonafluorobutyl)trifluorophosphate, etc.); antimonates (e.g.,hexafluoroantimonate); alum inates (e.g., tetrachloroaluminate); fattyacid carboxylates (e.g., oleate, isostearate, pentadecafluorooctanoate,etc.); cyanates; acetates; and so forth, as well as combinations of anyof the foregoing.

Several examples of suitable ionic liquids may include, for instance,spiro-(1,1′)-bipyrrolidinium tetrafluoroborate, triethylmethyl ammoniumtetrafluoroborate, tetraethyl ammonium tetrafluoroborate,spiro-(1,1′)-bipyrrolidinium iodide, triethylmethyl ammonium iodide,tetraethyl ammonium iodide, methyltriethylammonium tetrafluoroborate,tetrabutylammonium tetrafluoroborate, tetraethylammoniumhexafluorophosphate, etc.

As indicated above, the ultracapacitor of the present invention alsocontains a first current collector and a second current collector. Itshould be understood that additional current collectors may also beemployed if desired, particularly if the ultracapacitor includesmultiple energy storage cells. The current collectors may be formed fromthe same or different materials. Regardless, each collector is typicallyformed from a substrate that includes a conductive metal, such asaluminum, stainless steel, nickel, silver, palladium, etc., as well asalloys thereof. Aluminum and aluminum alloys are particularly suitablefor use in the present invention. The substrate may be in the form of afoil, sheet, plate, mesh, etc. The substrate may also have a relativelysmall thickness, such as about 200 micrometers or less, in someembodiments from about 1 to about 100 micrometers, in some embodimentsfrom about 5 to about 80 micrometers, and in some embodiments, fromabout 10 to about 50 micrometers. Although by no means required, thesurface of the substrate may be optionally roughened, such as bywashing, etching, blasting, etc.

In certain embodiments, at least one of the first and second currentcollectors, and preferably both, also contain a plurality of fiber-likewhiskers that project outwardly from the substrate. Without intending tobe limited by theory, it is believed that these whiskers can effectivelyincrease the surface area of the current collector and also improve theadhesion of the current collector to the corresponding electrode. Thiscan allow for the use of a relatively low binder content in the firstelectrode and/or second electrode, which can improve charge transfer andreduce interfacial resistance and consequently result in very low ESRvalues. The whiskers are typically formed from a material that containscarbon and/or a reaction product of carbon and the conductive metal. Inone embodiment, for example, the material may contain a carbide of theconductive metal, such as aluminum carbide (Al₄C₃). Referring to FIG. 1,for instance, one embodiment of a current collector is shown thatcontains a plurality of whiskers 21 projecting outwardly from asubstrate 1. If desired, the whiskers 21 may optionally project from aseed portion 3 that is embedded within the substrate 1. Similar to thewhiskers 21, the seed portion 3 may also be formed from a material thatcontains carbon and/or a reaction product of carbon and the conductivemetal, such as a carbide of the conductive metal (e.g., aluminumcarbide).

The manner in which such whiskers are formed on the substrate may varyas desired. In one embodiment, for instance, the conductive metal of thesubstrate is reacted with a hydrocarbon compound. Examples of suchhydrocarbon compounds may include, for instance, paraffin hydrocarboncompounds, such as methane, ethane, propane, n-butane, isobutane,pentane, etc.; olefin hydrocarbon compounds, such as ethylene,propylene, butene, butadiene, etc.; acetylene hydrocarbon compounds,such as acetylene; as well as derivatives or combinations of any of theforegoing. It is generally desired that the hydrocarbon compounds are ina gaseous form during the reaction. Thus, it may be desired to employhydrocarbon compounds, such as methane, ethane, and propane, which arein a gaseous form when heated. Although not necessarily required, thehydrocarbon compounds are typically employed in a range of from about0.1 parts to about 50 parts by weight, and in some embodiments, fromabout 0.5 parts by weight to about 30 parts by weight, based on 100parts by weight of the substrate. To initiate the reaction with thehydrocarbon and conductive metal, the substrate is generally heated inan atmosphere that is at a temperature of about 300° C. or more, in someembodiments about 400° C. or more, and in some embodiments, from about500° C. to about 650° C. The time of heating depends on the exacttemperature selected, but typically ranges from about 1 hour to about100 hours. The atmosphere typically contains a relatively low amount ofoxygen to minimize the formation of a dielectric film on the surface ofthe substrate. For example, the oxygen content of the atmosphere may beabout 1% by volume or less.

The ultracapacitor of also contains first and second carbonaceouscoatings that are electrically coupled to the first and second currentcollectors, respectively. While they may be formed from the same ordifferent types of materials and may contain one or multiple layers,each of the carbonaceous coatings generally contains at least one layerthat includes activated particles. In certain embodiments, for instance,the activated carbon layer may be directly positioned over the currentcollector and may optionally be the only layer of the carbonaceouscoating. Examples of suitable activated carbon particles may include,for instance, coconut shell-based activated carbon, petroleum coke-basedactivated carbon, pitch-based activated carbon, polyvinylidenechloride-based activated carbon, phenolic resin-based activated carbon,polyacrylonitrile-based activated carbon, and activated carbon fromnatural sources such as coal, charcoal or other natural organic sources.

In certain embodiments, it may be desired to selectively control certainaspects of the activated carbon particles, such as their particle sizedistribution, surface area, and pore size distribution to help improveion mobility for certain types of electrolytes after being subjected toone or more charge-discharge cycles. For example, at least 50% by volumeof the particles (D50 size) may have a size in the range of from about0.01 to about 30 micrometers, in some embodiments from about 0.1 toabout 20 micrometers, and in some embodiments, from about 0.5 to about10 micrometers. At least 90% by volume of the particles (D90 size) maylikewise have a size in the range of from about 2 to about 40micrometers, in some embodiments from about 5 to about 30 micrometers,and in some embodiments, from about 6 to about 15 micrometers. The BETsurface may also range from about 900 m²/g to about 3,000 m²/g, in someembodiments from about 1,000 m²/g to about 2,500 m²/g, and in someembodiments, from about 1,100 m²/g to about 1,800 m²/g.

In addition to having a certain size and surface area, the activatedcarbon particles may also contain pores having a certain sizedistribution. For example, the amount of pores less than about 2nanometers in size (i.e., “micropores”) may provide a pore volume ofabout 50 vol. % or less, in some embodiments about 30 vol. % or less,and in some embodiments, from 0.1 vol. % to 15 vol. % of the total porevolume. The amount of pores between about 2 nanometers and about 50nanometers in size (i.e., “mesopores”) may likewise be from about 20vol. % to about 80 vol. %, in some embodiments from about 25 vol. % toabout 75 vol. %, and in some embodiments, from about 35 vol. % to about65 vol. %. Finally, the amount of pores greater than about 50 nanometersin size (i.e., “macropores”) may be from about 1 vol. % to about 50 vol.%, in some embodiments from about 5 vol. % to about 40 vol. %, and insome embodiments, from about 10 vol. % to about 35 vol. %. The totalpore volume of the carbon particles may be in the range of from about0.2 cm³/g to about 1.5 cm³/g, and in some embodiments, from about 0.4cm³/g to about 1.0 cm³/g, and the median pore width may be about 8nanometers or less, in some embodiments from about 1 to about 5nanometers, and in some embodiments, from about 2 to about 4 nanometers.The pore sizes and total pore volume may be measured using nitrogenadsorption and analyzed by the Barrett-Joyner-Halenda (“BJH”) techniqueas is well known in the art.

As discussed above, one unique aspect of the present invention is thatthe electrodes need not contain a substantial amount of bindersconventionally employed in ultracapacitor electrodes. That is, bindersmay be present in an amount of about 60 parts or less, in someembodiments 40 parts or less, and in some embodiments, from about 1 toabout 25 parts per 100 parts of carbon in the first and/or secondcarbonaceous coatings. Binders may, for example, constitute about 15 wt.% or less, in some embodiments about 10 wt. % or less, and in someembodiments, from about 0.5 wt. % to about 5 wt. % of the total weightof a carbonaceous coating. Nevertheless, when employed, any of a varietyof suitable binders can be used in the electrodes. For instance,water-insoluble organic binders may be employed in certain embodiments,such as styrene-butadiene copolymers, polyvinyl acetate homopolymers,vinyl-acetate ethylene copolymers, vinyl-acetate acrylic copolymers,ethylene-vinyl chloride copolymers, ethylene-vinyl chloride-vinylacetate terpolymers, acrylic polyvinyl chloride polymers, acrylicpolymers, nitrile polymers, fluoropolymers such aspolytetrafluoroethylene or polyvinylidene fluoride, polyolefins, etc.,as well as mixtures thereof. Water-soluble organic binders may also beemployed, such as polysaccharides and derivatives thereof. In oneparticular embodiment, the polysaccharide may be a nonionic cellulosicether, such as alkyl cellulose ethers (e.g., methyl cellulose and ethylcellulose); hydroxyalkyl cellulose ethers (e.g., hydroxyethyl cellulose,hydroxypropyl cellulose, hydroxypropyl hydroxybutyl cellulose,hydroxyethyl hydroxypropyl cellulose, hydroxyethyl hydroxybutylcellulose, hydroxyethyl hydroxypropyl hydroxybutyl cellulose, etc.);alkyl hydroxyalkyl cellulose ethers (e.g., methyl hydroxyethylcellulose, methyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose,ethyl hydroxypropyl cellulose, methyl ethyl hydroxyethyl cellulose andmethyl ethyl hydroxypropyl cellulose); carboxyalkyl cellulose ethers(e.g., carboxymethyl cellulose); and so forth, as well as protonatedsalts of any of the foregoing, such as sodium carboxymethyl cellulose.

If desired, other materials may also be employed within an activatedcarbon layer of the first and/or second carbonaceous coatings and/orwithin other layers of the first and/or second carbonaceous coatings.For example, in certain embodiments, a conductivity promoter may beemployed to further increase electrical conductivity. Exemplaryconductivity promoters may include, for instance, carbon black, graphite(natural or artificial), graphite, carbon nanotubes, nanowires ornanotubes, metal fibers, graphenes, etc., as well as mixtures thereof.Carbon black is particularly suitable. When employed, conductivitypromoters typically constitute about 60 parts or less, in someembodiments 40 parts or less, and in some embodiments, from about 1 toabout 25 parts per 100 parts of the activated carbon particles in acarbonaceous coating. Conductivity promotes may, for example, constituteabout 15 wt. % or less, in some embodiments about 10 wt. % or less, andin some embodiments, from about 0.5 wt. % to about 5 wt. % of the totalweight of a carbonaceous coating. Activated carbon particles likewisetypically constitute 85 wt. % or more, in some embodiments about 90 wt.% or more, and in some embodiments, from about 95 wt. % to about 99.5wt. % of a carbonaceous coating.

The particular manner in which a carbonaceous coating is applied to acurrent collector may vary as is well known to those skilled in the art,such as printing (e.g., rotogravure), spraying, slot-die coating,drop-coating, dip-coating, etc. Regardless of the manner in which it isapplied, the resulting electrode is typically dried to remove moisturefrom the coating, such as at a temperature of about 100° C. or more, insome embodiments about 200° C. or more, and in some embodiments, fromabout 300° C. to about 500° C. The electrode may also be compressed(e.g., calendered) to optimize the volumetric efficiency of theultracapacitor. After any optional compression, the thickness of eachcarbonaceous coating may generally vary based on the desired electricalperformance and operating range of the ultracapacitor. Typically,however, the thickness of a coating is from about 20 to about 200micrometers, 30 to about 150 micrometers, and in some embodiments, fromabout 40 to about 100 micrometers. Coatings may be present on one orboth sides of a current collector. Regardless, the thickness of theoverall electrode (including the current collector and the carbonaceouscoating(s) after optional compression) is typically within a range offrom about 20 to about 350 micrometers, in some embodiments from about30 to about 300 micrometers, and in some embodiments, from about 50 toabout 250 micrometers.

A separator is also employed in the ultracapacitor that is positionedbetween the first and second electrodes. If desired, other separatorsmay also be employed in the ultracapacitor of the present invention. Forexample, one or more separators may be positioned over the firstelectrode, the second electrode, or both. The separators enableelectrical isolation of one electrode from another to help prevent anelectrical short, but still allow transport of ions between the twoelectrodes. In certain embodiments, for example, a separator may beemployed that includes a cellulosic fibrous material (e.g., airlaidpaper web, wet-laid paper web, etc.), nonwoven fibrous material (e.g.,polyolefin nonwoven webs), woven fabrics, film (e.g., polyolefin film),etc. Cellulosic fibrous materials are particularly suitable for use inthe ultracapacitor, such as those containing natural fibers, syntheticfibers, etc. Specific examples of suitable cellulosic fibers for use inthe separator may include, for instance, hardwood pulp fibers, softwoodpulp fibers, rayon fibers, regenerated cellulosic fibers, etc.Regardless of the particular materials employed, the separator typicallyhas a thickness of from about 5 to about 150 micrometers, in someembodiments from about 10 to about 100 micrometers, and in someembodiments, from about 20 to about 80 micrometers.

The ultracapacitor of the present invention employs a housing withinwhich the electrodes, electrolyte, and separator are retained andoptionally hermetically sealed. To enhance the degree of hermeticsealing, the housing generally contains a metal container (“can”), suchas those formed from tantalum, niobium, aluminum, nickel, hafnium,titanium, copper, silver, steel (e.g., stainless), alloys thereof,composites thereof (e.g., metal coated with electrically conductiveoxide), and so forth. Aluminum is particularly suitable for use in thepresent invention. The metal container may have any of a variety ofdifferent shapes, such as cylindrical, D-shaped, etc.Cylindrically-shaped containers are particular suitable.

The manner in which these components are inserted into the housing mayvary as is known in the art. For example, the electrodes and separatormay be initially folded, wound, or otherwise contacted together to forman electrode assembly. The electrolyte may optionally be immersed intothe electrodes of the assembly. In one particular embodiment, theelectrodes, separator, and optional electrolyte may be wound into anelectrode assembly having a “jelly-roll” configuration. Referring toFIG. 3, for instance, one embodiment of such a jellyroll electrodeassembly 1100 is shown that contains a first electrode 1102, secondelectrode 1104, and a separator 1106 positioned between the electrodes1102 and 1104. In this particular embodiment, the electrode assembly1100 also includes another separator 1108 that is positioned over thesecond electrode 1104. In this manner, each of two coated surfaces ofthe electrodes is separated by a separator, thereby maximizing surfacearea per unit volume and capacitance. While by no means required, theelectrodes 1102 and 1104 are offset in this embodiment so as to leavetheir respective contact edges extending beyond first and second edgesof the first and second separators 1106 and 1108, respectively. Amongother things, this can help prevent “shorting” due to the flow ofelectrical current between the electrodes.

The electrode assembly may be sealed within the cylindrical housingusing a variety of different techniques. Referring to FIG. 4, oneembodiment of an ultracapacitor is shown that contains an electrodeassembly 2108, which contains layers 2106 wound together in a jellyrollconfiguration as discussed above. In this particular embodiment, theultracapacitor contains a first collector disc 2114, which contains adisc-shaped portion 2134, a stud portion 2136, and a fastener 2138(e.g., screw). The collector disc 2114 is aligned with a first end of ahollow core 2160, which is formed in the center of the electrodeassembly, and the stud portion 2136 is then inserted into an opening ofthe core so that the disc-shaped portion 2134 sits against the first endof the electrode assembly 2108 at a first contact edge 2110. A lid 2118is welded (e.g., laser welded) to a first terminal post 2116, and asocket, which may be for example, threaded, is coupled to the fastener2138. The ultracapacitor also contains a second collector disc 2120,which contains a disc-shaped portion 2142, a stud portion 2140, and asecond terminal post 2144. The second collector disc 2120 is alignedwith the second end of the hollow core 2160, and the stud portion 2140is then inserted into the opening of the core so that the collector discportion 2142 sits against the second end of the electrode assembly 2108.

A metal container 2122 (e.g., cylindrically-shaped can) is thereafterslid over the electrode assembly 2108 so that the second collector disc2120 enters the container 2122 first, passes through a first insulatingwasher 2124, passes through an axial hole at an end of the container2122, and then passes through a second insulating washer 2126. Thesecond collector disc 2120 also passes through a flat washer 2128 and aspring washer 2130. A locknut 2132 is tightened over the spring washer2130, which compresses the spring washer 2130 against the flat washer2128, which in turn is compressed against the second insulating washer2126. The second insulating washer 2126 is compressed against theexterior periphery of the axial hole in the metal container 2122, and asthe second collector disc 2120 is drawn by this compressive force towardthe axial hole, the first insulating washer 2124 is compressed betweenthe second collector disc 2120 and an interior periphery of the axialhole in the container 2122. A flange on the first insulating washer 2124inhibits electrical contact between the second collector disc 2120 and arim of the axial hole. Simultaneously, the lid 2118 is drawn into anopening of the container 2122 so that a rim of the lid 2118 sits justinside a lip of the opening of the container 2122. The rim of the lid2118 is then welded to the lip of the opening of the container 2122.

Once the locknut 2132 is tightened against the spring washer 2130, ahermetic seal may be formed between the axial hole, the first insulatingwasher 2124, the second insulating washer 2126, and the second collectordisc 2120. Similarly, the welding of the lid 2118 to the lip of thecontainer 2122, and the welding of the lid 2118 to the first terminalpost 2116, may form another hermetic seal. A hole 2146 in the lid 2118can remain open to serve as a fill port for the electrolyte describedabove. Once the electrolyte is in the can (i.e., drawn into the canunder vacuum, as described above), a bushing 2148 is inserted into thehole 2146 and seated against a flange 2150 at an interior edge of thehole 2146. The bushing 2148 may, for instance, be a hollow cylinder inshape, fashioned to receive a plug 2152. The plug 2152, which iscylindrical in shape, is pressed into a center of the bushing 2148,thereby compressing the bushing 2148 against an interior of the hole2146 and forming a hermetic seal between the hole 2146, the bushing2148, and the plug 2152. The plug 2152 and the bushing 2148 may beselected to dislodge when a prescribed level of pressure is reachedwithin the ultracapacitor, thereby forming an overpressure safetymechanism.

The embodiments described above generally refer to the use of a singleelectrochemical cell in the capacitor. It should of course beunderstood, however, that the capacitor of the present invention mayalso contain two or more electrochemical cells. In one such embodiment,for example, the capacitor may include a stack of two or moreelectrochemical cells, which may be the same or different.

The resulting ultracapacitor can still exhibit excellent electricalproperties. For example, the ultracapacitor may exhibit a capacitance ofabout 6 Farads per cubic centimeter (“F/cm³”) or more, in someembodiments about 8 F/cm³ or more, in some embodiments from about 9 toabout 100 F/cm³, and in some embodiments, from about 10 to about 80F/cm³, measured at a temperature of 23° C., frequency of 120 Hz, andwithout an applied voltage. The ultracapacitor may also have a lowequivalence series resistance (“ESR”), such as about 150 mohms or less,in some embodiments less than about 125 mohms, in some embodiments fromabout 0.01 to about 100 mohms, and in some embodiments, from about 0.05to about 70 mohms, determined at a temperature of 23° C., frequency of100 kHz, and without an applied voltage.

Notably, the ultracapacitor may also exhibit excellent electricalproperties even when exposed to high temperatures. For example, theultracapacitor may be placed into contact with an atmosphere having atemperature of from about 80° C. or more, in some embodiments from about100° C. to about 150° C., and in some embodiments, from about 105° C. toabout 130° C. (e.g., 85° C. or 105° C.). The capacitance and ESR valuescan remain stable at such temperatures for a substantial period of time,such as for about 100 hours or more, in some embodiments from about 300hours to about 5000 hours, and in some embodiments, from about 600 hoursto about 4500 hours (e.g., 168, 336, 504, 672, 840, 1008, 1512, 2040,3024, or 4032 hours).

In one embodiment, for example, the ratio of the capacitance value ofthe ultracapacitor after being exposed to the hot atmosphere (e.g., 85°C. or 105° C.) for 1008 hours to the capacitance value of theultracapacitor when initially exposed to the hot atmosphere is about0.75 or more, in some embodiments from about 0.8 to 1.0, and in someembodiments, from about 0.85 to 1.0. Such high capacitance values canalso be maintained under various extreme conditions, such as whenapplied with a voltage and/or in a humid atmosphere. For example, theratio of the capacitance value of the ultracapacitor after being exposedto the hot atmosphere (e.g., 85° C. or 105° C.) and an applied voltageto the initial capacitance value of the ultracapacitor when exposed tothe hot atmosphere but prior to being applied with the voltage may beabout 0.60 or more, in some embodiments from about 0.65 to 1.0, and insome embodiments, from about 0.7 to 1.0. The voltage may, for instance,be about 1 volt or more, in some embodiments about 1.5 volts or more,and in some embodiments, from about 2 to about 10 volts (e.g., 2.1volts). In one embodiment, for example, the ratio noted above may bemaintained for 1008 hours or more. The ultracapacitor may also maintainthe capacitance values noted above when exposed to high humidity levels,such as when placed into contact with an atmosphere having a relativehumidity of about 40% or more, in some embodiments about 45% or more, insome embodiments about 50% or more, and in some embodiments, about 70%or more (e.g., about 85% to 100%). Relative humidity may, for instance,be determined in accordance with ASTM E337-02, Method A (2007). Forexample, the ratio of the capacitance value of the ultracapacitor afterbeing exposed to the hot atmosphere (e.g., 85° C. or 105° C.) and highhumidity (e.g., 85%) to the initial capacitance value of theultracapacitor when exposed to the hot atmosphere but prior to beingexposed to the high humidity may be about 0.7 or more, in someembodiments from about 0.75 to 1.0, and in some embodiments, from about0.80 to 1.0. In one embodiment, for example, this ratio may bemaintained for 1008 hours or more.

The ESR can also remain stable at such temperatures for a substantialperiod of time, such as noted above. In one embodiment, for example, theratio of the ESR of the ultracapacitor after being exposed to the hotatmosphere (e.g., 85° C. or 105° C.) for 1008 hours to the ESR of theultracapacitor when initially exposed to the hot atmosphere is about 1.5or less, in some embodiments about 1.2 or less, and in some embodiments,from about 0.2 to about 1. Notably, such low ESR values can also bemaintained under various extreme conditions, such as when applied with ahigh voltage and/or in a humid atmosphere as described above. Forexample, the ratio of the ESR of the ultracapacitor after being exposedto the hot atmosphere (e.g., 85° C. or 105° C.) and an applied voltageto the initial ESR of the ultracapacitor when exposed to the hotatmosphere but prior to being applied with the voltage may be about 1.8or less, in some embodiments about 1.7 or less, and in some embodiments,from about 0.2 to about 1.6. In one embodiment, for example, the rationoted above may be maintained for 1008 hours or more. The ultracapacitormay also maintain the ESR values noted above when exposed to highhumidity levels. For example, the ratio of the ESR of the ultracapacitorafter being exposed to the hot atmosphere (e.g., 85° C. or 105° C.) andhigh humidity (e.g., 85%) to the initial capacitance value of theultracapacitor when exposed to the hot atmosphere but prior to beingexposed to the high humidity may be about 1.5 or less, in someembodiments about 1.4 or less, and in some embodiments, from about 0.2to about 1.2. In one embodiment, for example, this ratio may bemaintained for 1008 hours or more.

The present invention may be better understood with reference to thefollowing example.

Test Methods Equivalent Series Resistance (ESR)

Equivalence series resistance may be measured using a Keithley 3330Precision LCZ meter with a DC bias of 0.0 volts, 1.1 volts, or 2.1 volts(0.5 volt peak to peak sinusoidal signal). The operating frequency is 1kHz. A variety of temperature and relative humidity levels may betested. For example, the temperature may be 85° C. or 105° C., and therelative humidity may be 25% or 85%.

Capacitance

The capacitance may be measured using a Keithley 3330 Precision LCZmeter with a DC bias of 0.0 volts, 1.1 volts, or 2.1 volts (0.5 voltpeak to peak sinusoidal signal). The operating frequency is 120 Hz. Avariety of temperature and relative humidity levels may be tested. Forexample, the temperature may be 85° C. or 105° C., and the relativehumidity may be 25% or 85%.

EXAMPLE

The ability to form an electrochemical cell in accordance with thepresent invention was demonstrated. Initially, each side of two aluminumcurrent collectors (thickness of 12 to 50 μm) containing aluminumcarbide whiskers were coated with a mixture of 10-40 wt. % of activatedcarbon particles, 2-10 wt. % of a styrene-butadiene copolymer, and 5-40wt. % of sodium carboxymethylcellulose. The activated carbon particleshad a D50 size of about 5-20 μm and a BET surface area of about1300-2200 m²/g. The activated carbon particles contained pores with asize of less than 2 nanometers in an amount of less than 10 vol. %,pores with a size of 2 to 50 nanometers in an amount of about 40 to 70vol. %, and pores with a size of greater than 50 nm in an amount ofabout 20 to 50 vol. %. The thickness of each resulting coating was about12 to 200 μm. The electrodes were then calendered and dried under vacuumat a temperature of from 70° C. to 150° C. Once formed, the twoelectrodes were assembled with an electrolyte and separators (cellulosematerial having a thickness of 25 μm). The electrolyte contained5-azoniaspiro[4,4]-nonanetetrafluoroborate at a concentration of 1.05 to2.5 M in propylene carbonate. The resulting strip is cut into individualelectrodes and assembled by stacking electrodes alternately withseparators therebetween. Once the electrode stack is complete, allelectrode terminals are welded to a single aluminum terminal. Thisassembly is then put into a plastic/aluminum/plastic laminated packagingmaterial and all but one of the edges are heat sealed together. Next,the electrolyte is injected into the package through the open edge. Theelectrolyte-filled package is then put under vacuum and the final edgeis heat sealed to complete the finished package. The resulting cellswere formed and tested for ESR, capacitance, and volumetric efficiency.The results are set forth below in Tables 1-6:

TABLE 1 Average ESR (mohms) for 24 Samples at 0.0 Volt Bias Time (hrs) 0168 336 504 672 840 1008 1512 2040 3024 4032  85° C. 65 61 59 62 64 6364 64 62 62 64 105° C. 62 54 52 57 60 60 60 58 58 57 58

TABLE 2 Average Capacitance for 24 Samples at 0.0 Volt Bias Time (hrs) 0168 336 504 672 840 1008 1512 2040 3024 4032  85° C. F 2.1 2.0 2.0 2.01.9 1.9 1.9 2.0 2.0 2.0 1.9  85° C. F/cm³ 10.3 10.1 9.8 9.7 9.7 9.7 9.79.7 9.7 9.7 9.6 105° C. F 2.0 2.0 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.8105° C. F/cm³ 9.9 9.9 9.7 9.6 9.5 9.4 9.4 9.4 9.3 9.2 9.0

TABLE 3 Average ESR (mohms) for 16 Samples at 0.0 Volt Bias Time (hrs) 0168 336 504 672 840 1008 85° C., 85% 121 133 144 152 166 177 187Relative Humidity

TABLE 4 Average Capacitance for 16 Samples at 0.0 Volt Bias Time (hrs) 0168 336 504 672 840 1008 85° C., 85% F 1.5 1.2 1.1 1.2 1.1 1.1 1.1Relative Humidity 85° C., 85% F/cm³ 7.7 5.7 5.7 6.0 5.5 5.6 5.5 RelativeHumidity

TABLE 5 Average ESR (mohms) for 10 Samples at 2.1 Volt Bias Time (hrs) 0168 336 504 672 840 1008 85° C. 146 163 167 169 171 173 175

TABLE 6 Average Capacitance for 16 Samples at 2.1 Volt Bias Time (hrs) 0504 1008 85° C., 85% Relative Humidity F 2.0 1.8 1.7 85° C., 85%Relative Humidity F/cm³ 10.1 9.2 8.7

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. An ultracapacitor comprising: a first electrodethat comprises a first current collector electrically coupled to a firstcarbonaceous coating; a second electrode that comprises a second currentcollector electrically coupled to a second carbonaceous coating; aseparator positioned between the first electrode and the secondelectrode; a nonaqueous electrolyte that is in ionic contact with thefirst electrode and the second electrode, wherein the nonaqueouselectrolyte contains an ionic liquid that is dissolved in a nonaqueoussolvent at a concentration of 1.0 mole per liter or more, wherein thenonaqueous solvent has a boiling temperature of about 150° C. or more;and a housing within which the first electrode, the second electrode,the separator, and the electrolyte are retained, wherein the housingcontains a metal container.
 2. The ultracapacitor of claim 1, whereinthe nonaqueous solvent includes a cyclic carbonate.
 3. Theultracapacitor of claim 2, wherein the solvent includes propylenecarbonate.
 4. The ultracapacitor of claim 1, wherein the ionic liquidcontains a cationic species and a counterion.
 5. The ultracapacitor ofclaim 4, wherein the cationic species includes an organoquaternaryammonium compound.
 6. The ultracapacitor of claim 5, wherein theorganoquaternary ammonium compound has the following structure:

wherein m and n are independently a number from 3 to
 7. 7. Theultracapacitor of claim 1, wherein the ionic liquid includesspiro-(1,1′)-bipyrrolidinium tetrafluoroborate,spiro-(1,1′)-bipyrrolidinium iodide, or a combination thereof.
 8. Theultracapacitor of claim 1, wherein the ionic liquid is present at aconcentration of about 1.2 moles per liter or more.
 9. Theultracapacitor of claim 1, wherein the first current collector and thesecond current collector each contain a substrate that includes aconductive metal.
 10. The ultracapacitor of claim 9, wherein theconductive metal is aluminum or an alloy thereof.
 11. The ultracapacitorof claim 9, wherein the substrate of the first current collector, thesubstrate of the second current collector, or both has a thickness ofabout 200 micrometers or less.
 12. The ultracapacitor of claim 9,wherein a plurality of fiber-like whiskers project outwardly from thesubstrate of the first current collector, the substrate of the secondcurrent collector, or both.
 13. The ultracapacitor of claim 12, whereinthe whiskers contain aluminum carbide.
 14. The ultracapacitor of claim1, wherein the first carbonaceous coating, the second carbonaceouscoating, or both contain activated carbon particles.
 15. Theultracapacitor of claim 14, wherein at least 50% by volume of theactivated carbon particles have a size of from about 1 to about 30micrometers.
 16. The ultracapacitor of claim 14, wherein the activatedcarbon particles have a BET surface area of from about 900 m²/g to about2,000 m²/g.
 17. The ultracapacitor of claim 14, wherein the activatedcarbon particles contain a plurality of pores, wherein the amount ofpores having a size of about 2 nanometers or less is about 50 vol. % orless of the total pore volume, the amount of pores having a size of fromabout 2 nanometers to about 50 nanometers is about 20 vol. % to about 80vol. % of the total pore volume, and the amount of pores having a sizeof about 50 nanometers or more is from about 1 vol. % to about 50 vol. %of the total pore volume.
 18. The ultracapacitor of claim 1, wherein thefirst carbonaceous coating, the second carbonaceous coating, or bothcontain binders in an amount of about 15 wt. % or less.
 19. Theultracapacitor of claim 1, wherein the first electrode, the secondelectrode, or both have a thickness of from about 40 micrometers toabout 350 micrometers.
 20. The ultracapacitor of claim 1, wherein theseparator includes a cellulosic fibrous material.
 21. The ultracapacitorof claim 1, wherein the metal container has a cylindrical shape.
 22. Theultracapacitor of claim 1, wherein the first electrode, the secondelectrode, the electrolyte, and the separator are hermetically sealedwithin the housing.
 23. The ultracapacitor of claim 1, wherein the firstelectrode, the second electrode, and the separator are wound into anelectrode assembly having a jellyroll configuration.